The overall objective of the proposed research is the elucidation of the biological behavior of low molecular weight transition metal complexes produced by microorganisms. Specifically the ability of some of these complexes, which contain the hydroxamate or alpha-diimine ligand system, to behave as microbial iron or cobalt transport agents will be studied. Certain aspects of the mechanism of antibiotic action of metal complexes, which contain the thiohydroxamate or o-nitrosophenol ligand system, will be studied. Uptake studies of radioactively labeled complexes will be undertaken to determine if their antibiotic activity can be correlated with their uptake.